1. Referring to someone or something that is hard to predict; irregular; erratic: Sometimes teachers can be termed as inconsistent when their expectations of their students vary from day to day.
2. Concerning statements which are not compatible with a further claim or fact: When Jack was called to give evidence, his interpretation of the accident was completely inconsistent and contrary with what the photos showed and what the police officer reported.
3. Pertaining to something which is contradictory with another part: When the Smiths were on their vacation, they came to an intersection which was totally inconsistent to the map they were using!